More than 91% of party's state committee members voted to support her at a meeting in Albany on Saturday.
The endorsement also means that Nixon will be on the November general election ballot even if she does not win the democratic nomination.
But in 2014, the party started to fracture as some liberal groups grew disenchanted with Cuomo's moderate record and his relationship with Republicans who control the state Senate.
The New York Timesreports that Cuomo has also been telling unions to cut off funding for community groups that veer for Nixon, and if they don't they can "lose my number".
Although Nixon's campaign has been seen as a long shot, obtaining one of the most sought-after endorsements might make her a more serious challenger to the two-time governor.
As governor, Cynthia would fight for a progressive agenda in NY by supporting policies to provide health care for all, legalize marijuana, and take corporate money out of politics. Cuomo soon followed to say he too would not seek the party's nod.
She cited his efforts to move NY toward a $15 an hour minimum wage, adopt same-sex marriage, enact paid family leave and achieve a record $27 billion in funding for education.
She announced her campaign in mid-March, running left of 2-term Governor Andrew Cuomo. Despite the attention here campaign's received online, most polls show her trailing Cuomo by almost 50 points.
Nixon is probably best known for playing Miranda Hobbes on HBO's "Sex and the City".